RAMALLAH, West Bank, March 13 (Reuters) - Palestinian President Mahmoud Abbas has accused one of his main rivals, Mohammed Dahlan, of involvement in six murders, hinting that he might also be behind the death of former leader Yasser Arafat.

Dahlan, who lives in exile in the Gulf, denied the allegations of his arch foe Abbas, their bitter row now playing out publicly across the Palestinian media and on social media.

Once a prominent official in Abbas's Western-backed Fatah movement, Dahlan was ousted from the group in 2011 following accusations of corruption. He denied the charges and remains a powerful figure on the sidelines, forging ties with numerous Arab leaders and maintaining links with the splintered Fatah.

Abbas lashed out at Dahlan, who is regularly cited as a possible future president, during a Fatah meeting earlier this week, with his comments later released to the press.

Abbas said an investigation was carried out into Dahlan, for years Fatah's strongman in the Gaza Strip, during the rule of former president Arafat. "It was found out that six people were killed by orders from Dahlan," the president said.

He added that Arafat had decided not to release the report. The iconic Palestinian leader died in mysterious circumstances in 2004 and many of his supporters are certain he was poisoned.

Abbas said he did not have any proof that Dahlan was involved, but he read out several statements in which his 52-year-old rival had allegedly criticised Arafat.

"Who killed Yasser Arafat? This is not evidence, but indications that deserve consideration," said Abbas, who has faced criticism from many Palestinians for pursuing apparently gridlocked peace negotiations with Israel.

"LIES, STUPIDITY, IGNORANCE"

An angry Dahlan hit back on his Face Book page, saying Abbas's speech was full of "lies ... stupidity and ignorance of the Palestinian reality." He added that he would also "unveil the lies" surrounding the death of Arafat, calling it "the most important and most dangerous issue of our modern history."

In an indication of growing sensitivity over Dahlan, Abbas's government earlier this month cut the salaries of nearly 100 security men still loyal to him in an apparent effort to undermine his popularity.

Arab media have reported in recent months that Dahlan has met Egypt's powerful army chief Field Marshal Abdel Fattah al-Sisi and has also reached out to Hamas, the Islamist rulers of Gaza who have always viewed him with deep distrust.

Perhaps seeking to exacerbate tensions between the two, Abbas said Dahlan had known of an Israeli plot to kill Hamas chief armed commander Salah Shehada. The assassination attempt failed, Abbas said.

Shehada died in an Israeli bombing and it was not clear what assassination attempt Abbas was referring to.

Dahlan said there was only ever one attack on Shehada and accused Abbas of making up stories.

Hamas spokesman Sami Abu Zuhri said Abbas's comments made clear the Palestinian leadership had conspired against his group, which ousted Fatah from Gaza after a 2007 civil war. (Writing by Nidal Almughrabi, edited by Crispian Balmer and Ralph Boulton)